This disclosure pertains to an apparatus and a method of shaping a laser beam profile for transmission via a LIDAR transmitter.
Light detection and ranging (LIDAR) is an optical remote sensing technology that measures properties of scattered light to find range and/or other information of a distant target. In LIDAR, a laser beam is often used to determine the distance to an object or to collect other information on the object. For example, the range to an object is determined by measuring the time delay between transmission of a laser pulse and detection of the reflected signal.
LIDAR is similar in many aspects to Radar technology. For example both LIDAR and Radar use radiation to project on an object and detect reflected radiation from the object. The primary difference is that LIDAR uses radiation with much shorter wavelengths. Typically, LIDAR uses near infrared, visible or ultraviolet radiation. The shorter wavelengths used in LIDAR allow measurement of smaller sized objects or object characteristics with higher resolution. Hence, LIDAR can be used for making measurements of smoke and other airborne particles (aerosols, clouds, and air molecules). For example, parameters such as the height, layering and densities of clouds, cloud particle properties (extinction coefficient, backscatter coefficient, depolarization), temperature, pressure, wind, humidity, trace gas concentration (ozone, methane, nitrous oxide, etc.) can be measured using LIDAR.
In general, lasers having a Gaussian intensity profile obtained by operating the lasers in the TEA00 fundamental mode are often utilized in a LIDAR system. However, the use of a Gaussian profile in a LIDAR transmitter can have numerous drawbacks. For example, as illustrated in FIG. 1 which depicts a conventional Gaussian profile in a LIDAR transmitter compared to an ideal top hat profile, excess energy (E) may be received at the center of a receiver detector focal plane array (FPA), i.e., received at the center of the field of view (FOV) of the detector FPA, while much less energy is received at the edge of the FPA detector. Furthermore, as shown in FIG. 1, energy in the side wings of the Gaussian beam falls outside the projection of the field of view (FOV) of the FPA detector as compared with an ideal top hat profile which provides the needed amount of energy for the detector to output a meaningful signal. As a result, the side wings' energy is wasted. In addition, as shown in FIG. 1, a large transmitter-to-receiver (T/R) boresight error is typically allocated which leads to additional inefficiency in the LIDAR system.
Therefore, there is a need in the art for a laser beam shaping apparatus that can produce a top hat intensity beam profile to efficiently use the laser energy.